1. Field of the Invention
This invention relates to air staged premixed dry low NO.sub.x gas turbine combustors of the type that are constructed with a fuel/air premixing chamber, a centerbody flame stabilizer and a venturi modulated flow split. Such structures of this type achieve stable combustion at a wide range of fuel-to-air ratios and low flame temperatures in the combustor resulting in low emissions of nitrogen oxides (NO.sub.x).
2. Description of the Related Art
It is known, in combustor systems, that in order to reduce NO.sub.x emissions, the maximum flame temperature in the combustor must be reduced. A well known method of reducing the flame temperature is to premix the fuel and the air prior to the mixture being combusted. However, it is also known that a premixed combustor, typically, runs over a relatively narrow operation window which is determined by lean blow-out at low-fuel/air ratios and high NO.sub.x emissions at high fuel/air ratios. Flame stability is very sensitive to fuel-to-air ratios and fuel/air velocity. For example, if the velocity of the mixture is too high, the flame in the combustor can be blown out. But, if the velocity is too low, the flame may propagate backwards into the premixing area which is commonly referred to as flashback. Also, if the fuel-to-air ratio is not properly maintained and the flame temperature gets too high, the amount of NO.sub.x created will increase which is also highly undesirable. Finally, due to the fact that almost all of the air introduced into the combustor is taken up by the head end of the combustor, very little air is capable of reaching the combustion chamber liner in order to cool the liner which can adversely affect the structural properties of the liner. Therefore, a more advantageous premixed low NO.sub.x combustor, then, would be presented if the combustor could be run over a larger operation window and the proper amount of air could be provided to the liner in order to cool the liner.
It is apparent from the above that there exists a need in the art for a premixed low NO.sub.x combustor which is efficient through simplicity of parts and uniqueness of structure, and which at least equals the NO.sub.x emissions characteristics of known premixed combustors, but which at the same time can be run over a larger operation window while still properly cooling the liner. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.